nowaytia-ga,
You've asked a question with no clear-cut answer.
There are many different forms of arsenic, different routes of
exposures, and different things that happen once it enters the body.
A short-term exposure to arsenic is very different, in terms of bodily
concentrations, than a long-term exposure.
As such, there are no well-documented criteria by which one can say
that X concentration in the blood or hair resulted from ingesting Y
amount of arsenic.
There is some overall perspective that I can provide, however. But
first, please take note of the disclaimer on the bottom of the page.
Google Answers is no substitute for professional medical advice, and
if you have concerns about exposure to arsenic, please seek medical
attention as soon as possible.
A very comprehensive overview of the known literature on arsenic
exposures was prepared a few years ago by the National Academy of
Sciences/National Research Council:
http://darwin.nap.edu/books/0309063337/html
Arsenic in Drinking Water
1999
prepared by:
Subcommittee on Arsenic in Drinking Water
Committee on Toxicology
Board on Environmental Studies and Toxicology
Commission on Life Sciences
National Research Council
NATIONAL ACADEMY PRESS
Washington, DC
You can search through this book at the above link, and view it online
a page at a time, if that is of interest to you.
I excerpted some passages from the book that are most relevant to your
question, and these are posted below, along with my comments.
However, it's helpful first to take note of some different units in
use.
You asked your question in terms of micrograms/g, which is often
abbreviated with the Greek letter mu: µg/g
1 µg/g is the same as 1 milligram/kg (1 mg/kg) and is approximately
the same as 1 mg/L or 1000 µg/L.
Therefore, the arsenic concentrations you mentioned in your question
can be expressed as:
0.007microg/g = .007 mg/kg = approx 7 µg/L (blood)
0.05 microg/g = .05 mg/kg (hair)
===============
The National Academy study has sections that specifically cover what
is known (and unknown) about the relationships between hair and blood
concentrations, and exposures. I've excerpted these below, with my
own comments in brackets:
=====
http://darwin.nap.edu/books/0309063337/html/181.html
Arsenic In Blood
...Most of the absorbed inorganic and organic arsenic has a short
half-time in blood (see Chapter 5); arsenic concentrations in blood
are increased only for a very short time following absorption. If
exposure is continuous and steady, as is often the case with exposure
through drinking water, the blood arsenic concentration might reach a
steady-state and then reflect the degree of exposure.
[that is, blood concentrations wouldn't necessarily be a reliable
indicator of short-term exposure to arsenic, but over the long run,
are a better reflection of exposure]
...Data on concentrations of arsenic in blood in people with no known
exposure to arsenic cover quite a wide range- 0.3-2 µg/L
[Your question referenced a blood level of approx 7 µg/L, higher than
what would be expected in the "no known exposure" group]
...In subjects exposed to arsenic via drinking water, blood arsenic
concentrations are clearly increased and might reach several tens of
micrograms per liter (Heydorn 1970; Valentine et al. 1979; Vahter et
al. 1995). In people exposed to arsenic in drinking water (200 µg/L)
in northern Argentina, arsenic concentration in blood was about 10
µg/L on average (Vahter et al. 1995; Concha et al. 1998a,b). In
studies carried out in California and Nevada, an arsenic concentration
of 400 µg/L in the water corresponded to about 13 µg/L in the blood,
and 100 µg/L in the water corresponded to 3-4 µg/L in the blood
(Valentine et al. 1979). Obviously, compared with urine, blood is a
much less sensitive biomarker of exposure to arsenic via drinking
water.
[The level you mentioned of approx 7 µg/L would be consistent with
long-term ingestion of drinking water contaminated with about 100-200
µg/L of arsenic. Note, however, that urine concentrations are
considered a more reliable indicator than blood concentrations].
====
http://darwin.nap.edu/books/0309063337/html/182.html
Arsenic In Hair And Nails
...Arsenic concentrations are normally higher in hair and nails than
in other parts of the body because of the high content of keratin, the
SH groups of which might bind trivalent inorganic arsenic (Curry and
Pounds 1977; Hopps 1977; Hostýnek et al. 1993).
[Concentrations would be expected to be higher in hair than most other
areas of the body]
...The main disadvantage of using hair and nails as indicators of
exposure to arsenic is that the arsenic concentrations might be
influenced by external contamination via air, water, soaps, and
shampoos. That was clearly demonstrated in studies on people living
in Fairbanks, Alaska, where the water contained arsenic at 345 µg/L
(Harrington et al. 1978). One group of people drinking essentially
only bottled water, resulting in low concentrations of arsenic in
urine (average 43 µg/L), had high arsenic concentrations in hair
(average 5.7 µg/g). In areas with low concentrations of arsenic in
drinking water (less than 50 µg/L in water, 38 µg/L in urine), the
concentration in hair was 0.4 µg/g, on average. Thus, the
concentrations in hair varied by a factor of 14 at similar
concentrations in urine. Apparently, arsenic was bound to the hair
during washing with the arsenic-rich water.
[Arsenic in hair does not necessarily result from ingestion]
...In people with no known exposure to arsenic, the concentration of
arsenic in hair is generally 0.02-0.2 mg/kg
[The concentration you noted of .05 mg/kg is actually at the low end
of the "no known exposure" range, which quite a different result than
the blood numbers]
...On a group basis, a few reports indicate that the correlation
between the concentration of arsenic in drinking water and the
concentration in hair is fairly good, although it is not known how
much of the arsenic in hair originates from arsenic in blood and how
much is bound due to external contact with the water, as discussed
above. The range of reported relationships is significant.
...In studies carried out in California and Nevada, a concentration of
400 µg/L in drinking water corresponded to about 1.2 µg/g in hair, and
100 µg/L in water corresponded to about 0.5 µg/g in hair (Valentine et
al. 1979). In Alaska, an average of 400 µg/L in drinking water
corresponded to 3.3 µg/g in hair (Harrington et al. 1978). In Hungary,
people with drinking-water concentrations ranging from 50 to 100 µg/L
had an average hair concentration of 3 µg/g (Börzsönyi et al. 1992).
The highest hair arsenic concentrations were found in children. In
Canada, 50% of 86 individuals using well water with arsenic
concentrations above 50 µg/L had hair arsenic concentrations above 1
µg/g (Grantham and Jones 1977). Of the 33 people using wells with
arsenic concentrations above 100 µg/L, 94% had hair concentrations
above 1 µg/g...
[Contrary to the blood concentration numbers discussed above, the hair
concentration of .05 µg/g (.05 mg/kg) is consistent with low/no
exposure to arsenic.]
===============
In sum, the blood concentration data is consistent with arsenic
exposure in drinking water of about 100-200 µg/L. On the other hand,
the hair concentration data is not consistent with this level of
exposure. The reason for the inconsistency is not known, but bear in
mind that that there are many, many factors that can affect the
concentration numbers in hair and blood. There simply is no known way
to accurately and reliably translate these test results into a
conclusive assessment of arsenic ingestion.
I trust this is exactly the sort of information you need.
However, please don't rate this answer if there's anything more I can
do for you. Just post a Request for Clarification to let me know how
I can assist your further, and I'm at your service.
All the best,
pafalafa-ga
search strategy: Google search on [ arsenic pharmacokinetics OR biomarker ] |
